EP 0 320 987 B1 (Norsk Hydro, 1989) claims a conditioning agent for reducing dust formation and moisture uptake in a nitrate-containing fertilizer, comprising 10-60 weight % wax, 30-90 weight % oil and 0.3-10 weight % of a high-molecular viscoelastic elastomer which is soluble in oil and has an average molecular weight of 30.000-5.000.000. The preferred wax is a mixture of paraffin wax, polyethylene wax and microcrystalline wax. The preferred viscoelastic elastomer is polyisobutylene (PIB). This conditioning agent is usually applied in amounts of 0.3 weight %, with respect to the weight of the fertilizer and at normal humidities, it gives excellent results, even for hygroscopic fertilizers like CN. However, at humidities often occurring in tropical and subtropical areas, fertilizers coated with this agent, will absorb moisture in unacceptable amounts. Application of more than 0.5 weight % of the agent reduced the moisture absorption markedly, but the fertilizer became too sticky for being handled by conventional means.
EP 0 768 993 B1 (Norsk Hydro, 1997) again addressed the problem of reducing dust formation and hygroscopicity in particulate nitrate-containing fertilizer under tropical conditions. It was found that the reason for the tendency to stickiness was mainly related to the elastomer component in the conditioning agent. Accordingly, this component was substituted with a resin component having somewhat different properties, being oil-soluble and miscible with wax and oil. Hence, the patent claimed a conditioning agent for reducing dust formation and moisture uptake in nitrate-containing fertilizer, comprising 10-50 weight % wax, 40-90 weight % oil and 1-30 weight % of a resin being oil-soluble and miscible with wax and oil. The use of a viscoelastic elastomer component like polyisobutylene was discouraged. This coating is marketed by Yara International ASA under the trade name Tropicote™. The use of the elastomer component was marginally addressed in two similar patent documents WO 01/38263 A1 (Norsk Hydro, 2001) and EP 1 390 322 B1 (Yara International ASA, 2004), both dealing with the use of a bio-degradable conditioning agent comprising a vegetable oil, which is to be avoided in the current application, as well animal and marine oils because such oils will often cause an awful smell in tropical and subtropical environments.
WO 01/38263 addresses the problem of reducing hygroscopicity, caking and dust formation in particulate fertilizers such as NP, NPK, AN, CAN, urea, and other nitrogen-containing fertilizers. The patent document claims a conditioning agent, comprising 1-60 weight % wax, 5-90 weight % oil, which is a vegetable oil, an animal oil, or a marine oil, especially herring oil, and 5-90 weight % resin being oil-soluble and miscible with wax and oil, which is a fish oil distillation residue. Polyisobutylene, which is a bio-degradable elastomer, can optionally be added in an amount of 0 to 5 weight %. Example 5 shows a conditioning agent comprising 39.4 weight % wax, 34.6 weight % oil, 22.0 weight % resin and 4 weight % polyisobutylene.
Similarly, EP 1 390 322 addresses the problem of reducing caking and dust formation in particulate fertilizers such as NP, NPK, AN, CAN, urea, and other nitrogen-containing fertilizers. The patent document claims a conditioning agent, comprising 5-50 weight % wax, 5-75 weight % oil, which is a vegetable oil, an animal oil, or a marine oil, 0-60 weight % resin being oil-soluble and miscible with wax and oil, which is a fish oil distillation residue, and 2 to 15 weight % of a surface active agent, such as arylalkylsulphonate, phosphates, glutinates, or other anionic and/or cationic surface active agents. Polyisobutylene, which is a bio-degradable elastomer, can optionally be added in an amount of 0 to 5 weight %.